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Site Practice
Concrete Construction
Alistair Russell
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• Site practice affects finished product
• Handling & placing• Compaction & finishing• Curing• Cracking & expectations• Joints & tolerances
26 March 2015 Concrete Construction - Site Practice 2
Site Practice
Context: Concrete slabs
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• We have 4 courses on offer including a 2-day course devoted to just this topic – we can’t do that in 1 hour!
• Guide to Concrete Construction book –free
• Best practice video on YouTube – free
26 March 2015 Concrete Construction - Site Practice 3
CCANZ Courses
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• Starts as soon as concrete discharged from truck – 1st step in concrete’s life
• Move as quickly & efficiently as possible• Workable, without segregation – balance
26 March 2015 Concrete Construction - Site Practice 4
Handling & Placing
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• Get this right and the life of the structure will go well
• Get this wrong, and your life will not go well –compaction etc &remediation, cost…
26 March 2015 Concrete Construction - Site Practice 5
Handling & Placing
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26 March 2015 Concrete Construction - Site Practice 6
Primary Considerations
• Workability basically means how easy concrete is to use – and place
• More water = more workable
• Generally “runnier” concrete is easy to useTOO RUNNY = SEGREGATION
• Long term performance
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• Workability related to nature of job– Thin forms – more
workable concrete– Mass sections – less
workability required– Concrete pumps –
require a plastic and cohesive mix
26 March 2015 Concrete Construction - Site Practice 7
Workability (slump)
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• Avoiding Segregation• Aiding Compaction
• Correct term is “placing” not “pouring”– Implies some control over process
26 March 2015 Concrete Construction - Site Practice 8
Placing
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26 March 2015 Concrete Construction - Site Practice 9
Avoiding Segregation
Flatwork
General Principles• Whatever method,
place without delay• Deposit in face
already poured• Slopes-start at
bottom
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• Chutes• Barrows• Crane & skip or Bucket/skip• Pumps and Pipelines
• Concrete must be uniform and delivered at appropriate rate – x m3/hour
26 March 2015 Concrete Construction - Site Practice 10
Distribution Methods
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26 March 2015 Concrete Construction - Site Practice 11
Pumps and Pipelines
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• Specialised pumping operations• Notify concrete supplier of method of
placement – NZS 3109, 6.2• Pump mixes
– High slump– High(er) shrinkage– Not great off-form finish
26 March 2015 Concrete Construction - Site Practice 12
Pumps and Pipelines
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• Often compaction and finishing are part of the same operation– Often for flat work – flat horizontal surfaces
• Remember a smooth surface is not necessarily evidence of good compaction
26 March 2015 Concrete Construction - Site Practice 13
Compaction & Finishing
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26 March 2015 Concrete Construction - Site Practice 14
Compaction
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• Compaction enables concrete to reach:– Design strength– Density– Low permeability– Specified surface finish
• Compaction sometimes merges into finishing
26 March 2015 Concrete Construction - Site Practice 15
Compaction
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• Expel entrapped air• Pack aggregate particles• Increase
– Reinforcement bond– Ultimate strength– Abrasion resistance– Durability
• Minimise shrinkage and cracking
26 March 2015 Concrete Construction - Site Practice 16
Purpose of Compaction
Increases density
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• 2 stage process– Liquefaction occurs quickly– Expelling entrapped air more slow
• Compaction is complete when no more air bubbles rise to surface
26 March 2015 Concrete Construction - Site Practice 17
Process of Compaction
PROCESS: Liquefaction of the concrete which allows it to slump and fill the form
TIME: 3 to 5 seconds
PROCESS: The expulsion of air
TIME: 7 to 15 seconds
. Total time: 10-20 seconds
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26 March 2015 Concrete Construction - Site Practice 18
Effect on Hard Concrete
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26 March 2015 Concrete Construction - Site Practice 19
Finishing
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• While concrete is still plastic:– Levelling– Floating– Trowelling– Other treatments
• Purpose of finishing is to achieve:– Level or specified profile– Flatness– Surface density and texture
26 March 2015 Concrete Construction - Site Practice 20
Flatwork Finishing
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1. Screeding – hand/timber/mechanical screed
2. Floating– To level surface– Compact surface layers
3. Trowelling– To produce smooth, hard and durable
surface & densify surface
26 March 2015 Concrete Construction - Site Practice 21
Flatwork Finishing
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26 March 2015 Concrete Construction - Site Practice 22
Screeding
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• Even but open surface texture– Embed large particles– Remove imperfections– Compact and consolidate fines at surface– Close minor cracks
• When bleed water stops• Must be able to stand on concrete – minor
indentations
26 March 2015 Concrete Construction - Site Practice 23
Floating
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• Bull floating• Hand floating• Machine floating
26 March 2015 Concrete Construction - Site Practice 24
Floating
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• Final surface treatment– Working the surface– Compact top surface
• Delay between floating and trowelling– Stiffening of concrete
• Smoothness, density & wear resistance
26 March 2015 Concrete Construction - Site Practice 25
Trowelling
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• Flat blade – don’t create ripples• Subsequent trowels tilt the blade
– Once concrete is firm enough
• Blisters mean blade is too pitched• Blisters reduce durability + ugly
26 March 2015 Concrete Construction - Site Practice 26
Trowelling
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26 March 2015 Concrete Construction - Site Practice 27
Trowelling
Hand trowellingShould give a ringing sound
Machine trowellingRegular pattern
Hand trowel in corners
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26 March 2015 Concrete Construction - Site Practice 28
Trowelling
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26 March 2015 Concrete Construction - Site Practice 29
Trowelling
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• Footpaths, patios, paths & steps• Not in industrial floors – need crisp edge
26 March 2015 Concrete Construction - Site Practice 30
Edging
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26 March 2015 Concrete Construction - Site Practice 31
Curing
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• Cement hydration – chemical reaction– Requires water– Takes days, weeks– Starts fast, gets slower, will continue (forever)
• Curing – process of controlling loss of moisture– Allows time for hydration to occur
26 March 2015 Concrete Construction - Site Practice 32
Curing
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• Prevent loss of moisture– Leave formwork in place– Cover with impermeable membrane
• Continuously wetting surface– Ponding– Spraying
26 March 2015 Concrete Construction - Site Practice 33
Curing
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• Impermeable Membrane– Formwork– Plastic sheeting
• Water– Ponding– Sprinkling*
– Wet coverings• Accelerated curing
26 March 2015 Concrete Construction - Site Practice 34
Methods of Curing
*Water blaster spraying upwards into wind
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• Comprehensive physical barriers not always practical/economical
• Curing Compounds achieve same resultsSika Antisol®
• Apply after bleed water stops
• Be aware of coatings– Wax based – no painting– Resin based – ok to paint (acrylic)
26 March 2015 Concrete Construction - Site Practice 35
Curing Compounds
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• For appearance or function• Surface treatments depends on:
– Traffic & frequency– Chemicals– Impact loads
• Warehouse floors with steel wheel loads (forklifts) – high strength concrete– Specified by designer– Proper compaction, finishing and curing
26 March 2015 Concrete Construction - Site Practice 36
Surface Treatments
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• Densifiers – for polishing floors
26 March 2015 Concrete Construction - Site Practice 37
Polished Floors
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• Slip – for pedestrians• Skid – for wheels
• NZS 3114 defines surface finishes• F – Formed finish (from formwork)• U – Unformed finish (exposed to air)
26 March 2015 Concrete Construction - Site Practice 38
Slip & Skid
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• Slip – for pedestrians• Skid – for wheels
• NZS 3114 defines surface finishes
26 March 2015 Concrete Construction - Site Practice 39
Slip & Skid
F1 F6
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• Slip – for pedestrians• Skid – for wheels
• NZS 3114 defines surface finishes
26 March 2015 Concrete Construction - Site Practice 40
Slip & Skid
U2 U5
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• Examples U3 Trowelled Finish– Gradual variations limited to a maximum of 5
mm.– Abrupt variations limited to a maximum of 3
mm.
26 March 2015 Concrete Construction - Site Practice 41
Floor Tolerances
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Formed Finish Classification Hot Conditions
> 20°
AverageConditions≤ 20° > 12°
Cold Conditions≤ 12° > 5°
Beam and slab soffits
Forms 4 days 6 days 8 days
Supporting members (shores or backprops)
12 days 18 days 24 days
Vertical faces Finishes F6, F5, F4
1 day 2 days 3 days
Finishes F3, F2, F1
9 hours 12 hours 18 hours
A minimum of 2 days applied to the stripping of vertical faces where frost damage is likely.
26 March 2015 Concrete Construction - Site Practice 42
Formwork Removal
Table 5.3 NZS 3109 – minimum formwork stripping times for in situ concrete
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26 March 2015 Concrete Construction - Site Practice 43
Other Finishes
Exposed Aggregate
Brushed
Sand Blasted
Polished
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Exposed Aggregate
• Natural rounded coarse aggregate– Not quarried rock (too
jagged)• Chemical retarder on
surface– Apply after bleed stops– Before setting
• 20MPa (not 17.5MPa)– Reduces stone loss
26 March 2015 Concrete Construction - Site Practice 44
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Exposed Aggregate
• Surface retarder – e.g. Sika Rugasol®
• Delays hydration of cement for 3-6mm depth
• Garden sprayer• Uniform coverage is
essential• Retardation period ≤ 24h
– Wash off prior to set– Wash low pressure
26 March 2015 Concrete Construction - Site Practice 45
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Cracks in Concrete• Concrete has low tensile strength
0 – 24 hours - plastic shrinkage cracksprevent rapid moisture loss- plastic settlement cracksrevibrate concrete- thermal movement cracksuse low heat mix (eg flyash)
7 days – 2 years - restrained shrinkage crackingadequate reinforcingdetailing of movement joints
26 March 2015 Concrete Construction - Site Practice 46
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• Fill – well compacted and even• Control joints
– Saw cuts initiate cracking– 12–18 hours after finishing– Insert crack inducer
• Joint layout – 5m between (6m in NZS3604)
– Align with walls where possible– Square bays are best
26 March 2015 Concrete Construction - Site Practice 47
Crack Avoidance
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26 March 2015 Concrete Construction - Site Practice 48
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• Contraction Joints
• Expansion Joints
26 March 2015 Concrete Construction - Site Practice 49
Joints
Concrete shrinks 6 – 10mm per 10m length
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26 March 2015 Concrete Construction - Site Practice 50
Contraction Joints
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• Oxides – most coloured concrete– Mixing is important
• Spray on coloured compounds– Can fix as you go– Less durable
• Coloured concrete usually doesn’t affect the strength
26 March 2015 Concrete Construction - Site Practice 51
Coloured Concrete
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26 March 2015 Concrete Construction - Site Practice 52
Colouring Oxides
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• Powdered or liquids– Penetrate all through the concrete– Add to mixing concrete
• Peter Fell• Permacolour NZ• Rockwood – Elements and Atmospheric range
• Part of the specification• Seek expert advice• Beware multi-batch variations
26 March 2015 Concrete Construction - Site Practice 53
Colouring Oxides
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• IB 18: Architectural Surface Finishes• IB 33: Specification and Production of Concrete
Surface Finishes• IB 86: Self-Compacting Concrete
• CCANZ Concrete Construction Course 8-9 September, Auckland
www.ccanz.org.nz
26 March 2015 Concrete Construction - Site Practice 54
Further Reading
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Site Practice
Concrete Construction
Alistair Russell
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Baldev Kesha
Concrete Mix designs and Applications
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Concrete Standards
• NZS 3101 Concrete Structures- A Standard for designers
• NZS 3109 Concrete Construction- Should be on every job site outlines good construction practice.
• NZS 3104 Specification for Concrete Production-Outlines the quality controls rules for producing concrete.
• NZS 3121, NZS 3122, AS1478, Quality of materials which are use to make concrete
• NZS3111, NZS3112 Method of conducting tests to prove properties
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Basic concrete materials
• Portland – cement reacts with water to provide strength
• Sand (fine agg) – provides cohesion & workability
• Stone (coarse agg) – provides stiffness and limits movement
• Mixing water – provides lubrication and hydrates cement
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Chemical Admixtures
• Water reducers – improve dispersion and cut water content
• Air-entrainers – create micro-bubbles that improve
workability
• Accelerators – increase chemical reaction & reduce setting
time
• Retarders – decease chemical reaction & increase setting
time
• Pump aids – stabilisers that increase viscosity of concrete
• Shrinkage – reduce drying shrinkage of concrete
• Others – corrosion inhibitors, expansive agents, foamers59
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Supplementary Cementitious Materials (SCM’s)
• Flyash, fine ash from burning coal, supplied by GBC from Huntly.
• GGBS, Ground Granulated Blast Furnace Slag. Waste product from iron manufacture. Sold as Duracem as a Slag/GP blend 65/35.
• Microsilica- very fine natural silica sold by GBC.
All improve the durability of concrete but have differing characteristics.
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Other Materials
• Recycled slurry water: – Increasing plants are reusing washing water in concrete rather than disposing
• Steel and synthetic fibres:– Increasing demand for fibre reinforcedconcrete in floor slabs, tunneling & mining
• Surface treatments, pigments – Aesthetics of concrete is critical for somearchitectural projects
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Components of Concrete
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Concrete performance
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Fresh propertiesFirst 6-10 hours
Hardened propertiesNext 50-100 years
WorkabilityBleedingPumpabilityFinishabilitySetting time
StrengthDurabilityStabilityAesthetics
Performance
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Components of Concrete
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Concrete performance
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Fresh propertiesFirst 6-10 hours
Hardened propertiesNext 50-100 years
WorkabilityBleedingPumpabilityFinishabilitySetting time
StrengthDurabilityStabilityAesthetics
Performance
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Displays
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Making Samples
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Kerikeri Stone Store – Historicalsite
Fontera – ColaberationInternal and External finishesClient, Architect, Interior Designer, Landscape Architect,Main contractor, Placer
We will endeavour to find a suitable site to view
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Muriwai Atmospheric Black
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Silverdale Shopping Centre –Concrete tells a History story
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Waikato University
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Speights Ale House - Nelson
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ASB Black Polished Floor
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Tait - Christchurch
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Thank you
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